The present invention relates to a three-port junction receiver acting as a direct receiver, a receiving method, a calibration method for a three-port junction device as well as a telecommunications device comprising such a receiver.
From the state of the art the six-port technology is known, which has been used up to recent years for complex measurements and can also be utilized for the reception and detection of RF-signals. Said technique is generally described, for example, in EP-A-0 805 561. A six-port receiver acts in the direct conversion manner allowing conversion from mm-wave range and microwave range directly to the baseband. At the same time a classic I/Q demodulation chip (digital or analog) can be avoided. By using suitable calibration procedures the influences of the non-ideal passive RF components including manufacturing tolerances can be minimized. The six-port receiver detects the relative phase and the relative magnitude of two incoming RF signals. The circuitry of the six-port receiver is realized using only passive components in combination with diodes for the detection of the relative phase and the relative magnitude of the RF signals. An important feature of six-port receivers is that fabrication tolerances can compensated for by a calibration, which inherently allows low-cost production. A further example for a six-port receiver is proposed in Bossisio, Wu xe2x80x9cA six-port direct digital mm-wave receiverxe2x80x9d, Digest of 1994, IEEE MTT symposium, Vol.3, p. 1659-1662, San Diego, May 1994.
The main feature of the six-port receiver is that it performs a detection of the vector ratio between two incoming vector signals by means of a power sensing device.
The disadvantage of the six-port technology, however, is that it requires four power sensors and complicated calibration procedures.
Therefore, it is the object of the present invention to provide a technique which, is as effective as the six-port technique, but which can be implemented in a less complicated way and requires only a simplified calibration procedure.
Said object of the invention is achieved by means of the features of the independent claims. The dependent claims develop further the central idea of the invention.
According to the present invention a direct receiver for digital modulated RF-signals is provided, wherein the direct receiver comprises only one passive three-port circuitry. A first port of the passive three-port circuitry thereby is supplied with a received digital RF signal. A second port of the passive three-port circuitry is connected to a power sensor, wherein the power sensor generates an output signal which can be further processed after DC filtering. Input selection means are provided for inputting one of a plurality of predetermined signals to a third port of the passive three-port circuitry.
A local oscillator is provided being selectively connectable with a third port of the passive three-port circuitry by means of the input selection means.
The input selection means can be a switch selectively connecting an output signal of the local oscillator or a ground potential with the third port of the passive three-port circuitry.
The switch can have three switching positions, wherein in a first position a first output of the local oscillator is connected with a third port of the passive three-port circuitry, in a second position a second output the second output of the local oscillator is connected with a third port of the passive three-port circuitry, and in a third switching position said ground potential is connected to the third port of the passive three-port circuitry. At least one LO output is phase-shifted before being supplied to the RF switch. Thereby the second output of the local oscillator is phase shifted by at least one phase shifting means relatively to the first output of the local oscillator.
A termination resistor is connected to ground in one switching position.
The switch can have a maximum switching frequency such that it is adapted to switch at least three times per state duration (duration of a modulation bit) of the received digital modulated RF signal.
A second switch can be provided for routing an output of the local oscillator to one or more of a plurality of phase shifters, wherein each of said plurality of phase shifters provides for a different phase shift amount.
The second switch thereby has a maximum shifting frequency such that it is adapted to switch at least two times per modulation state duration (duration of a modulation bit) of the received digital modulated RF signal.
The detection time of the power sensor is less than one third of the state duration (duration of a modulation bit) of the received digital modulated RF signal.
The output of the power sensor is supplied to the DC interface after being DC filtered. The analog processing board is attached to the DC interface. Alternatively a fast A/D converter is attached to the DC interface.
A DC switch can be connected between the power sensor and the plurality of delay lines, wherein the switching of the DC switch is effected synchronously to the switching of the first mentioned switch.
The output of the power sensor is supplied by means of at least one A/D converter to a digital processing unit detecting the IQ components of the received digital modulated RF signal.
The conversion rate of the A/D converter is at least three times higher than the inverse of a modulation state duration (duration of a modulation bit) of the received digital modulated RF signal.
The passive three-port circuitry can be implemented by a plurality of technologies, e.g. by resistors, by a microstrip technology or a coplanar waveguide technology.
A low-pass filter is provided between the output side of the power sensor and the DC interface.
According to the present invention a mobile communications device is provided comprising a direct receiver as set forth. The mobile communications device particularly can be a mobile terminal of a private or public telecommunications network.
According to the present invention furthermore a method for calibrating a direct receiver with the features as set forth above is provided, wherein a RF signal modulated with a predefined known sequence is fed through the first port of the passive three-port circuitry.
According to another aspect of the present invention a method for directly receiving digital modulated RF signals is provided. A digital modulated RF signal is supplied to a first port of a passive three-port circuitry. The power level of a second port of the passive three-port circuitry is detected to generate an output signal, which can be further processed for example to detect I/Q components. One of a plurality of predetermined signals is selectively input to a third port of the passive three-port circuitry.
The step of selectively inputting can comprise the step of selectively inputting an output of a local oscillator to the third port of the passive three-port circuitry.
The step of selectively inputting can comprise the steps of inputting an output signal of the local oscillator and a step of supplying a ground potential to the third port of the passive three-port circuitry.
The step of selectively inputting can comprise particularly in a time-multiplex manner the following steps:
a) supplying said ground potential to the third port of the passive three-port circuitry,
b) inputting a first output of the first output of the local oscillator to the third port of the passive three-port circuitry, and
c) inputting a second output of the local oscillator to the third port of the passive three-port circuitry,
wherein the second output of the local oscillator is phase shifted relatively to the first output of the local oscillator.
Respectively one sequence of the above-mentioned steps a), b) and c) is effected per state duration of the received digital modulated RF signal. Note that the order of the above steps can set arbitrarily and can be modified from time to time.
The detection time of the power sensor is less than one third of the state duration (duration of a modulation bit) of the received digital modulated RF signal.
The output of the power sensor is processed in an analog manner to detect the I/Q components of the received digital modulated RF signal.
The output of the power sensor can be supplied to the analog processing selectively with a predetermined delay out of a number of predefined delays in a time multiplex manner.
The predetermined delay can be changed synchronously to the step of selectively inputting one of a plurality of predetermined signals to a third port of the passive three-port circuitry.
The output of a power sensor can be low-pass filtered and A/D converted and digitally processed to detect the I/Q components of the received digital modulated RF signal (or can be directly digitally processed to obtain the modulation states).
The A/D conversion (sampling) speed of the direct digital processing is three times faster compared to the speed of a A/D converter in the case of a classical analog I/Q demodulator.
The detected power level is low-pass filtered.
Further advantages, features and effects of the present invention will come clearer from the following description of embodiments taking in conjunction with the figures to the enclosed drawings.